The International Agency for Research in Cancer (IARC) has recently assigned indoor tanning to its highest cancer risk category, carcinogenic to humans, joining asbestos, tobacco, arsenic and mustard gas. A comprehensive meta-analysis concluded that the risk of melanoma increased by 75% when indoor tanning is initiated before 30 years old. Melanoma incidence is rising faster than any other cancer with an estimated 60,000 diagnoses annually in the US. Despite this, indoor tanning is gaining tremendous popularity, especially among youth. Recent reviews report approximately 10% of US adolescents under the age of 15 have used indoor tanning in the past year, with prevalence among older adolescent females estimated at 25-40%. There is evidence that female indoor tanning use increases dramatically from freshman to senior years of high school (HS) making high school a critical time period for anti-tanning interventions to be implemented. This proposal assesses the efficacy of a skin cancer prevention program that will be delivered via the Internet to a nationally representative sample of high school teens in a randomized controlled trial. The anti-tanning intervention has proven success in reducing UV risk behaviors across multiple trials and multiple sites over the past 8 years with adult samples when delivered via a booklet. Our research will identify HS females at risk for future UV risk behavior (i.e., current users plus women indicating strong intentions to initiate indoor tanning in the next 6 months), and provide them with persuasive information on the appearance damaging effects of UV exposure, delivered via an attractive, user friendly website. The intervention is based on proven theories of health behavior change (i.e., behavioral alternatives model, social cognitive theory, theory of reasoned action and protection motivation theory), and formative research in high school samples. A national, award-winning web development team will produce the website which will be beta tested with groups of teen tanners to ensure congruence with current teen culture, values and beliefs. The research team has successfully worked with the web-development team and with teen testers to produce and modify a prototype of the intervention which has proven to be relevant and of interest to teen tanners in pilot studies. The proposal uses practices that ensure intervention fidelity and assessments of intervention dosage. We will follow these women from HS through post-HS to examine whether the intervention is able to reduce the overall frequency of long-term UV exposure. The intervention is cost-effective, can be easily disseminated and is likely to be engaging for the targeted teen audience. If successful, wide dissemination of this intervention is likely to substantially reduce indoor tanning initiation and use in high school teens and thus the future occurrence of and mortality from melanoma and non- melanoma skin cancers in this population. The investigative team has the experience and skills needed to successfully complete all aspects of the research, and the approach has been used successfully in previously funded projects. The study is innovative. It will be the first anti-tanning intervention directed at high school students, the first appearance-focused intervention targeting HS tanners, the first Internet-delivered intervention focusing on skin cancer risk behavior in teens, and the first using a nationally representative sample. There is a strong rationale for the use of an appearance-based, Internet delivered intervention with long-term follow-up targeting high school students. High school represents a critical developmental stage for both melanoma risk (i.e., risk appears to increase with indoor tanning in youth) and for the development of regular, frequent intentional UV exposure through tanning. Empirical results testing our conceptual model of teen tanning provides evidence that changing the key cognitive variables in the intervention will reduce tanning motivations and behaviors in teens. An Internet-delivered intervention can be easily and cheaply disseminated, and will be well received by the targeted teen population.